The invention relates to a tape or strip unreeling device and its application to a tape reader or playback means.
A tape unreeling device makes it possible to transfer a tape wound onto a storage reel to a receiving reel and vice versa. In general, the tape comprises a data carrier on which analog or digital data can be recorded, played back or read and optionally erased. Such data carriers are known in various forms, e.g. photographic films, magnetic tapes, perforatable tapes, etc. As a function of the use of the tape unreeling device, the tape movement can be continuous, intermittent or jerky, as in cinematography technology. In addition, in certain applications, the tape unreeling device must operate in the two directions of movement, or at least must have the capacity to rewind the tape onto the storage reel. Tape unreeling devices of this type are known, particularly those used in cinematographic projection equipment.
There are two types, namely those having lateral insertion mainly used for 35 mm films and those with so-called automatic insertion for 8 mm or super 8 films. In the first type, after the operator has positioned the storage reel and after opening a lateral door, he inserts the leader of the film between the guide rollers and pulleys. He then attaches the leader of the film to the mandrel of the take-up reel. However, this operation is long and complex.
In the second type, the operator inserts the leader of the film in a slot, the film perforations engage with a toothed wheel, which transports the leader of the film in accordance with a given circuit. This leader is fastened to the take-up reel by wedging of the lateral flanges and then by friction between successive turns. However, there is frequently a risk of deterioration of the leader of the film and sometimes of the film itself as a result of untimely sliding and the poor engagement of the leader during its manual insertion. Moreover, this type of equipment requires relatively rigid films.
A tape reader makes it possible to read or even analyse data recorded on a support wound onto a reel. Various types of tape readers exist, particularly photographic film tape readers on which data are recorded in the form of contiguous images or pictures which are analysed by television scanning and are then displayed on the surface of a cathode ray tube.
The standard analysis procedure used is the flying spot process in which an extremely thin pencil of light scans the film surface. The light which passes through the film is trapped by a photoelectric cell in the case of monochrome pictures, or after separating the fundamental components of the light by means of a plurality of photoelectric cells in the case of polychrome pictures.
Unlike in cinematographic projection equipment in which the film strip moves in a jerky manner, in picture or image strip reading equipment, such as telecine equipment, the strip advances in a regular manner at a clearly defined speed, which greatly simplifies the equipment from the electronic standpoint compared with shooting cameras, but leads to mechanical problems. Thus, it is necessary to very accurately unwind the strip and modify the displacement of the light beam in order to compensate for the actual movement of the film. It is very difficult to obtain the required precision in view of the mechanical tolerances in connection with the production of the film, possible deterioration to the lateral transport perforations, sticking and contraction phenomena caused by temperature variations and the relative humidity of the air.
Another type of tape reader is encountered in the navigation field, particularly the field of aircraft navigation. In this type of tape reader, the tape is a data carrier, generally in the form of a photographic film on which are recorded pictures arranged in a predetermined order. These pictures correspond to maps of the regions which are liable to be overflown. The unwinding of the film is synchronous with the speed component of the aircraft, in accordance with one of the two coordinates of the map and the pencil of light of the film reader only analyses part of the picture and is displaced transversely and synchronously with the aircraft speed in accordance with the other coordinate of the map. Appropriate means make it possible to provide that part of the film corresponding to the geographical position of the aircraft in the reading channel of the reader. This tape reader is associated with a cathode ray tube cartographic indicator. In this type of tape reader, the strip of film is of large size and a large amount of data is recorded. The position of the pictures in the reading channel must be very accurately known. It must be possible for the strip or tape to unwind in both directions. The film strip must be changeable as required and the insertion of the start of the film must take place automatically.
Other types of equipment incorporating tape or strip unreeling means are in particular recorders on data carrier strips or tapes used in optical line scanning sensors, side beam radar equipment, sonar equipment, etc.
Thus, there is a very considerable demand for devices making it possible to unwind a tape on which is stored a large amount of data, i.e. a tape of considerable length and width able to record a large amount of data per surface unit. Thus, to permit the production of reels or spools having limited overall dimensions, the tape must have a limited thickness, so that it is more fragile and more difficult to insert in the device and in addition the high data density involves a precise guidance of the tape, the minimizing of mechanical clearances and the measurement of the position of the tape in the reading channel with a small error. Moreover, it is desirable for the tape to be inserted automatically onto the guide pulleys, into the reading channel and onto the receiving reel.